platform/vcs-impl/src/com/intellij/openapi/vcs/impl/CollectionsDelta.java

/*
 * Copyright 2000-2009 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.intellij.openapi.vcs.impl;

import org.jetbrains.annotations.Nullable;

import java.util.Collection;
import java.util.HashSet;
import java.util.Set;

public class CollectionsDelta {
  private CollectionsDelta() {
  }

  @Nullable
  public static <T> Set<T> notInSecond(final Collection<T> first, final Collection<T> second) {
    Set<T> notInSecond = null;
    for (T topItem : first) {
      if (! second.contains(topItem)) {
        if (notInSecond == null) {
          notInSecond = new HashSet<T>();
        }
        notInSecond.add(topItem);
      }
    }
    return notInSecond;
  }
}